1. Field of the Invention
This invention relates to disposable diapers, and more particularly to disposable diapers which are capable of arresting a leakage of urine and other fluids discharged from the body in the waist part and preventing diaper rash in the waist part, and which have improved strength and enhanced fit to the wearer in the waist portion.
2. Description of the Prior Art
It is well known that conventional paper diapers (disposable diapers) are generally superior to cloth diapers in adsorbability, in water retentivity and in a capacity of waste materials. Examples of known disposal diapers are disclosed in Japanese Laid-open Publications Nos. 58-54002, 59-144601, 60-17101, 62-223303 and 61-275402.
Japanese Laid-open Publication No. 58-54002 discloses a disposable diaper which has a liquid pervious topsheet, a liquid impervious backsheet and a water impermeable plastic sheet interposed between both sheets at the edge of the absorbent core in the waist part to thereby prevent urine and other fluids leaking from the edge of the absorbent core.
Japanese Laid-open Publication Nos. 59-144601 and 60-17101 disclose disposable diapers which have an elastically expansible member of heat contractibility around the waist part thereby improving the fit with the waist portion and protecting an undergarment from wetting with a leakage of urine and other fluids.
Japanese Laid-open Publication No. 62-223303 discloses a disposable diaper which has an elastically expansible member of polyurethane foam around the waist part to thereby enhance the fit. This disposable diaper intends to prevented waste materials from wetting the undergarment when tucking clothes, especially an undergarment, between the front waist flap part and the infant's body.
Japanese Laid-open Publication No. 61-275402 discloses a disposable diaper which adapts the advantages of the above-mentioned two disposable diapers. Between a liquid permeable topsheet and a liquid impermeable backsheet, at least one unitary waistshield and an elastically expansible waistband are interposed thereby preventing the fluids which migrate toward the perimeter of the diaper from wetting the wearer's undergarment.
However, the disposable diaper disclosed in Japanese Laid-open Publication No. 58-54002 has such a problem that a space occurs around the waist portion depending on the wearing condition of an infant, and if the waist portion is so fastened as not to provide a space, the infant receives pressure. Further, even if there is no space, the infant may move so hard that the figure of the infant changes according to the physical activity or movements, and a diaper will become out of shape and slip out of place. Thus a space occurs around the waist portion, and urine and other fluids are liable to leak due to the lack of the fit to the waist portion of the infant.
Recently, as a backsheet, a vapor pervious film tends to be used for preventing stuffiness; the vapor pervious film being obtained by stretching polyolephin resin to which an inorganic filler is added. However, the strength in the lateral direction of disposable diapers is low, and the strength in the lateral direction of nonwoven fabric generally used as a topsheet is low, too. Therefore, a problem occurs when the adhesive tape of the diaper is tightly stretched or the waist size expands according to the activity, a tension works on both of the back and top- sheets to tear the sheets longitudinally. In this case, even if a vapor pervious barrier sheet comprising the same material as a backsheet is placed to attempt to enhance the strength, the tension works on the non-connected portion of the topsheet, the barrier sheet and the backsheet, and the barrier sheet intermediate resists the tension. Therefore, it is a problem that when the lateral strength of the barrier sheet is low, even the barrier sheet tears and a leakage occurs.
In each of the disposable diapers disclosed in Japanese Laid-open Publications Nos. 59-144601 and 60-17101, an elastically expansible member is so interposed in the lateral direction between the topsheet and the backsheet as to ventilate and prevent stuffiness. However, it is a problem that urine and other fluids are likely to leak from the ventilation part and a leakage out of the waist portion cannot be prevented.
The disposable diaper disclosed in Japanese Laid-open Publication No. 62-223303 can prevent an undergarment from wetting when the undergarment is tucked into the space between the diaper and the body. However, it is a problem that urine and other fluids cannot be efficiently prevented from leaking out of the edge of the absorbent core.
It is a problem of the disposable diaper disclosed in Japanese Laid-open Publication No. 61-275402 that the waist gather in the waistband part does not fit so closely to the waist portion as to prevent urine and other fluids from leaking out of the absorbent core. Therefore, urine and other fluids are liable to leak through the waist gather part, and the intended object cannot be completely achieved.